I was supposed to be running in this year's New York Marathon, but injury brought my training to a shuddering halt. To say I was disappointed to have to pull out (even if the many people in my position do get to defer their entry to next year) is typically-English understatement, so when the opportunity arose to ride the 26.2-mile runner's course on my bike on race day, I jumped at it.

I still had a smidgeon of envy for the runners, as New York dawned in perfect conditions, chilly but brilliant, on Sunday morning. But I couldn't be churlish about it for long: after all, how many people get to parade on their bike for the whole closed-road course, complete with cheering crowds?

The answer is about 70 people have that unusual privilege – although no one is cheering for us, the cyclists, because rightly, they're yelling encouragement to the wheelchair racers, whom the cyclists accompany as outriders.

The way it works is this: the wheelchair racers set off early, before the elite runners start, and even though the course is all laid out and barricaded off, there is still the chance that some sleepy pedestrian or misdirected motorist will venture onto the course. The wheelchair racers can hit 30mph on the downhill sections and they're low to the ground, not necessarily visible at first glance, so their safety depends on the course really being clear in front of them. So, since 2003, when this first became a concern, a group of volunteer cyclists has been marshalled to provide a pair of escorts for each wheelchair racer.

The guy who organises these outriders is a character named Richard Rosenthal, a septuagenarian former president of the New York Cycling Club and marketing consultant. According to one of Rosenthal's amusing pre-Marathon day emails, we were a richly varied cross-section of New Yorkers united by a love of biking:

After riding out from Manhattan and through Brooklyn, this diverse peloton assembled on a flyover just off the down-ramp from the Verrazano Bridge, where the Marathon starts on the Staten Island side. We took our assignments and lined up on either side of the road, armed with a whistle and a luminous bib announcing our status as official escorts. A little before 9am, the first men came tearing around the corner and the first batch of cyclists set off, flanking them.

You've seen the machines in Paralympic races: they're three-wheelers, with a small wheel in front that is steerable and has a brake. The racer sits, pitched forward, with their arms working over two larger wheels that are canted inwards towards their armpits. Each wheel has an inner ring on the outside, which is where the racer applies force to rotate the wheels. The first impression I had, watching the men racers, was "My God, that looks hard work: I can't believe they can keep up that work rate for a mile, let alone 26.2!" But they do. These are astonishing athletes: the best in the world come to compete in the New York Marathon.

As soon as the road tilts upwards, they have to work constantly, and with no gearing, the speed drops to 14-15mph. But on the flat, or down hill, gravity works in their favour, and they can keep up 20-25mph with just an occasional big push and an aerodynamic tuck. Wheelchair racers are also allowed to "draft" off each other, slipstreaming – just like cyclists in a race. Small groups form and the racing becomes somewhat tactical – although, in the end, stamina and strength decide it.

I was held back for the women wheelchair racers, tasked with accompanying the first female racer. This turned out to be a terrific opportunity – giving me and my co-escort, Megan, a fast-moving grandstand seat for American athlete Amanda McGrory's course record-setting win in a time of 1:50:24. Somewhere between Brooklyn and Queens, around mile 10, McGrory started to pull out a lead from an elite group of four, which had formed in the first few miles. By the time she hit the killingly long grade up over the 59th Street Bridge into Manhattan, at about mile 16, before a loop takes the race into the Bronx and back towards the finale in Central Park, McGrory was overhauling some of the male racers.

She kept up a relentless pace, rhythmically churning those wheels with long flailing movements of her arms. It was a deeply impressive performance. My only regrets were not being allowed to join the crowds urging her on; but we riders were briefed to stay silent and impartial – these are world-class athletes, we were reminded; don't distract them because they're not here to chat with us. I only heard McGrory speak once – to check whether a male wheelchair racer who had stopped to repair a puncture to one of his wheels was OK.

I couldn't believe she even had the breath to do that. But it tells you plenty about what sort of competitors these wheelchair racers are. For a cyclist, it was both a humbling and an inspiring experience – and a day I'll remember long after I've forgotten everything about the New York Marathon I hope to run myself.